IA32: printing FP register variables

[Joern Rennecke]

> STABS's live range splitting notation can certainly do the job
> correctly, but I wonder whether it can do it efficiently.  For every
> instruction that changes TOP, you have to start a new range for every
> variable.  So the size of debug info is O(number of insns * average
> number of live variables).

You only have to care about variables that are live in the register stack
before or after the operation.  So you can use an upper bound of 8.
Hence the deubg info is O(number of insns).